It has been known that a metal oxide film is formed using a so-called atomic layer deposition (ALD) method on a semiconductor wafer (hereinafter, referred to as a “wafer”) supported in the shape of a shelf on a wafer boat within a reaction vessel of a vertical heat treatment apparatus. For example, an ALD process of forming a zirconium oxide (ZrO2) film by alternately supplying a raw material gas formed of a zirconium (Zr) compound and an ozone (O3) gas as an oxidation gas has been proposed.
In this process, a step of supplying the raw material gas into the process vessel, a step of supplying the oxidation gas into the process vessel and a step of purging the interior of the process vessel between the step of supplying the raw material gas and the step of supplying the oxidation gas are set as an one-time film forming operation, and the film forming operation is repeated a plurality of times to form a ZrO2 film having a predetermined thickness. In this manner, when the raw material gas and the oxidation gas are switched, the interior of the process vessel is substituted with the purge gas. When the substitution is insufficient, an amount of impurities may be increased in the ZrO2 film or coverage performance may be degraded.
Therefore, it is necessary to optimize the substitution conditions, and this operation is performed for each process type, which is complicated. In addition, even though appropriate substitution conditions are set, a phenomenon that the film quality of the obtained ZrO2 film is unintentionally degraded may occur during the course of repeatedly performing the film forming process within the process vessel.
In another related art, a method of recognizing an ending point of purge processing by measuring a moisture concentration of a gas discharged from a reaction chamber has been known as a purging method of an MOCVD apparatus. However, this method is intended to ensure that the purge processing is performed within a short time, while suppressing a waste of an alkyl metal used in the purge processing, but even the use of this technique cannot solve a technical problem of the present disclosure.